Add Plotting + Chart Library

[johannes-wolf]

This PR adds a plotting plot, chart, axes and palette library.

[fenjalien]

Could these options be set through style, if the fill is none the filling operation doesn't occur?

[johannes-wolf]

I was wondering how to use style in code where we have no context, as we can not get inherited style values. This means using style would not work as expected.

I have changed this a bit in the new version.

[fenjalien]

I was thinking a bit more about this and I think we have a children-ctx key that should be a function that accepts ctx. We could allow a group's body be that function.

[johannes-wolf]

This is already possible, by just passing a function to a group.
But how should e.g. epigraph be set? like set-style(plot: (epigraph: red))?

[fenjalien]

The api feels a lot cleaner now and wow thoughs graphs :) However it would be good to get the styling to work in a similar manner to set-style.

I've focused my review mostly on the design of the api in the manual. I don't mind how its been implemented in the lib files unless there is something specific you want me to look over.

[fenjalien]

I don't think having the return type array is very clear as we don't explain anywhere that actually the draw functions return arrays that implicitly get joined. I also think we should rename content to body as you can't use Typst's content. Maybe just say "body can also be function takes a single parameter, a dictionary that describes the group's current context such as styling".

We should also start making some separate developer documentation for the context dictionary but I'm not to bothered about it right now.

[johannes-wolf]

Yeah, but we should first generate function docs from the code doc. I do not like having both.

[fenjalien]

Could the axes use a similar input to styling? As in nested dictionaries:

plot(
  axes: (
    x: (
      label: "X",
      ...
     ),
    y: ...
  )
)

You could then allow options to be applied to both axes by allowing them in the base of the axes dict or through a default dict.

plot(
  axes: (
   // Applies to all axes
  ticks: ...
   // or if you want to keep axis names clear
   default: (
      ticks: ...
    ),
   // An axis
    y: ...
  )
)

This might even allow them to be set through set-style?t

[fenjalien]

You might also want to group tick options like step, minor-step, values etc.

[johannes-wolf]

I am not sure if that is good, as it comes with no real benefit. Tikz also uses this "flat" approach, which I find is fast to type and looks a bit cleaner.